From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0FE45C433B4 for ; Tue, 27 Apr 2021 12:43:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCF71613C6 for ; Tue, 27 Apr 2021 12:43:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237743AbhD0MoR (ORCPT ); Tue, 27 Apr 2021 08:44:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:47091 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237609AbhD0MoM (ORCPT ); Tue, 27 Apr 2021 08:44:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619527408; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=07wOgPW9dB/cel9XTXNEQi8cZjIP+YUY1hWOxH332nY=; b=ZtL9xOIsschrJ8v5YuRGgj1jsGIGk0OxSmruQJifSWmceqZqjuCCxa6LP3G1GbwDk3ZNJ2 sGVURK4/UKQ9o/soSBlQeqlkB2kjjVe+1aFWA3YGAKnm7fSwQLgTfIK3mCj452NERw7hKy 9fcDMuTVgpJBxYrgnyb2p2xjHcIXINU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-229-M9K6e4PCOSSJwhWL53KjTA-1; Tue, 27 Apr 2021 08:43:26 -0400 X-MC-Unique: M9K6e4PCOSSJwhWL53KjTA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AEFE36D241; Tue, 27 Apr 2021 12:43:24 +0000 (UTC) Received: from krava (unknown [10.40.192.237]) by smtp.corp.redhat.com (Postfix) with SMTP id E96906064B; Tue, 27 Apr 2021 12:43:22 +0000 (UTC) Date: Tue, 27 Apr 2021 14:43:22 +0200 From: Jiri Olsa To: Arnaldo Carvalho de Melo Cc: Andrii Nakryiko , Martin KaFai Lau , Jiri Olsa , dwarves@vger.kernel.org, bpf , Kernel Team , Andrii Nakryiko Subject: Re: [PATCH dwarves] btf: Generate btf for functions in the .BTF_ids section Message-ID: References: <20210423213728.3538141-1-kafai@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Apr 27, 2021 at 09:34:30AM -0300, Arnaldo Carvalho de Melo wrote: > Em Tue, Apr 27, 2021 at 01:38:20PM +0200, Jiri Olsa escreveu: > > On Mon, Apr 26, 2021 at 04:26:11PM -0700, Andrii Nakryiko wrote: > > > On Fri, Apr 23, 2021 at 2:37 PM Martin KaFai Lau wrote: > > > > BTF is currently generated for functions that are in ftrace list > > > > or extern. > > > > > > > > A recent use case also needs BTF generated for functions included in > > > > allowlist. In particular, the kernel > > > > commit e78aea8b2170 ("bpf: tcp: Put some tcp cong functions in allowlist for bpf-tcp-cc") > > > > allows bpf program to directly call a few tcp cc kernel functions. Those > > > > functions are specified under an ELF section .BTF_ids. The symbols > > > > in this ELF section is like __BTF_ID__func____[digit]+. > > > > For example, __BTF_ID__func__cubictcp_init__1. Those kernel > > > > functions are currently allowed only if CONFIG_DYNAMIC_FTRACE is > > > > set to ensure they are in the ftrace list but this kconfig dependency > > > > is unnecessary. > > > > > > > > pahole can generate BTF for those kernel functions if it knows they > > > > are in the allowlist. This patch is to capture those symbols > > > > in the .BTF_ids section and generate BTF for them. > > > > I wonder if we just record all functions how bad that would be. Jiri, > > > do you remember from the time you were experimenting with static > > > functions how much more functions we'd be recording if we didn't do > > > ftrace filtering? > > > hum, I can't find that.. but should be just matter of removing > > that is_ftrace_func check > > > if we decided to do that, maybe we could add some bit indicating > > that the function is traceable? it would save us check with > > available_filter_functions file > > You mean encoding it in BTF, in 'struct btf_type'? Seems important to > have it, there are free bits there: > > /* Max # of type identifier */ > #define BTF_MAX_TYPE 0x000fffff > /* Max offset into the string section */ > #define BTF_MAX_NAME_OFFSET 0x00ffffff > /* Max # of struct/union/enum members or func args */ > #define BTF_MAX_VLEN 0xffff > > struct btf_type { > __u32 name_off; > /* "info" bits arrangement > * bits 0-15: vlen (e.g. # of struct's members) > * bits 16-23: unused > * bits 24-27: kind (e.g. int, ptr, array...etc) > * bits 28-30: unused > * bit 31: kind_flag, currently used by > * struct, union and fwd > */ > __u32 info; > /* "size" is used by INT, ENUM, STRUCT, UNION and DATASEC. > * "size" tells the size of the type it is describing. > * > * "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT, > * FUNC, FUNC_PROTO and VAR. > * "type" is a type_id referring to another type. > */ > union { > __u32 size; > __u32 type; > }; > }; > > And tools that expect to trace a function can get that information from > the BTF info instead of getting some failure when trying to trace those > functions, right? yep, if it's possible to spare some bit for this info jirka